(1) Field of the Invention
This invention relates to temporary barriers which delay the contact of one reactant with another reactant in photographic elements and more particularly to color diffusion transfer film units wherein one portion of the film unit is temporarily isolated from another portion by a barrier layer comprising a mixture of (1) from 5 to 95 percent by weight of a copolymer comprising from 55 to 85 percent by weight of vinylidene chloride, 5 to 35 percent by weight of an ethylenically unsaturated monomer and 0 to 20 percent by weight of an ethylenically unsaturated carboxylic acid, and (2) from 5 to 95 percent by weight of a polymeric carboxy-ester-lactone.
(2) Description Relative to the Prior Art
Interlayers have been used in multicolor photographic elements to aid in differential processing of various silver halide emulsions after exposure and to minimize the effects of one layer of the element on another when both are simultaneously undergoing similar treatment as disclosed by Neblett, Photography, Its Materials and Processes, 1962, Chapter 33. The use of improved interlayers in a multicolor image transfer film unit is well known, for example, as disclosed in U.S. Pat. Nos. 3,411,904 and 3,418,117, both by Becker. The interlayers in many of the known film units act as temporary barriers to isolate the reactants of the surrounded layers for a predetermined length of time.
Image transfer processes are well known in the art which employ a single processing solution to develop an exposed image record and produce a viewable image record. In many instances, after-treatments such as washing or stabilizing baths are not used in these image transfer processes, since the element is a fully self-contained film unit.
In certain instances, various barrier layers, timing layers or spacer layers have been used in image transfer film units to delay action between the ingredients of various layers of the image transfer film unit. Barrier layers have been used between polymeric acid layers and the silver halide emulsion layers of an image transfer film unit to allow processing to continue at a high pH for a predetermined period of time before the acid layer becomes effective in neutralizing the processing composition as disclosed in U.S. Pat. No. 2,584,030, issued Jan. 29, 1952.
The use of barriers or spacer layers employed in conjunction with neutralizing layers in one commercial image transfer product is described by Friedman, History of Color Photography, 1968, pages 538 through 543. In products of this type, the alkaline composition penetrates through the barrier layer and alkali is depleted throughout the structure by the acid in the neutralizing layers. In certain instances, breakdown of the barrier layers releases materials which serve as a shutoff mechanism, establishing the amount of silver halide development and the related amount of dye formed according to the respective exposure values.
Various formats for color diffusion transfer assemblages are described in the prior art, such as U.S. Pat. Nos. 2,543,181; 2,983,606; 3,362,819; 3,362,821; 3,592,645; 3,785,815; 3,415,644; 3,415,645; 3,415,646; 3,647,437; 3,635,707 and 3,756,815, and Canadian Pat. Nos. 928,559 and 674,082. In these formats, the image-receiving layer containing the photographic image for viewing can be separated from the photographic layers after processing or, in some embodiments, it can remain permanently attached and integral with the image-generating and ancillary layers present in the structure when a transparent support is employed on the viewing side of the assemblage. The image is formed by color-providing substances released from the image-generating units, diffusing through the layers of the structure to the dye image-receiving layer. After exposure of the assemblage, an alkaline processing composition permeates the various layers to initiate development of the exposed photosensitive silver halide emulsion layers. The emulsion layers are developed in proportion to the extent of the respective exposures, and the image dyes which are formed or released in the respective image-generating layers begin to diffuse throughout the structure. At least a portion of the imagewise distribution of color-providing substances diffuse to the dye image-receiving layer to form an image of the original subject.
Various barrier layers for these purposes are described in U.S. Pat. Nos. 3,362,819; 3,455,686; 3,415,644; 3,414,411; 3,785;815; 3,575,701; 2,584,030; 3,421,893; 3,419,389; 3,433,633; 3,856,522; 4,056,394 and 4,061,496, and Canadian Pat. No. 928,559, and British Pat. No. 1,340,349.
Development can be carried out over a wide temperature range. At temperatures considerably less than room temperature which may be encountered in cold surroundings, the development process, which is temperature-dependent, is slower and a barrier layer which breaks down or is penetrated by an alkali using a less temperature-dependent process prevents sufficient development to achieve a discernible image. On the other hand, at temperatures considerably higher than room temperature, prior art barrier layers do not allow the reduction of pH soon enough, resulting in an overdevelopment of the emulsion layers.
In an image transfer process whereby diffusible dyes are released imagewise from immobile or nondiffusible dye-releasing compounds in the areas where development of silver takes place, underdevelopment provides a washed-out, low-density image in dyes in the receiving layer. Over-development results in overly dark images of high dye density.
Research Disclosure 12331, Volume 123, July 1974, entitled "Neutralizing Materials in Photographic Elements", cites a variety of polymers useful in timing layers, including poly(vinyl acetate-co-maleic anhydride) lactonized and esterified to form an intramolecular ester-lactone. However, the breakdown rate of the carboxy-ester-lactone barrier layer is somewhat less affected by temperature than is the sequence of reactions of photographic development. The value of the activation energy of penetration by alkali is about 16 kcal/mole as compared to 18 to 22 kcal/mole for that of the photographic sequence of reactions. Thus, shutdown at high temperatures is not rapid enough to completely avoid overdevelopment, and shutdown at lower temperatures is not slow enough to completely avoid underdevelopment.
In U.S. Pat. No. 4,056,394, issued Nov. 1, 1977, Hannie describes a barrier layer which has improved temperature flexibility with respect to its ability to shut down development. The Hannie barrier layer comprises a polymeric latex having an activation energy of penetration by aqueous alkaline solution of greater than 18 kcal/mole. Preferred polymer latices comprise terpolymers of from 5 to 35 percent by weight of polymerized ethylenically unsaturated monomer, from about 2 to 10 percent by weight of ethylenically unsaturated carboxylic acid, and from 55 to 85 percent by weight of polymerized vinylidene chloride. This barrier layer allows the neutralizing layer to shut down development at a later time at low temperatures and earlier at high temperatures. However, at high temperatures, its dependence with respect to photographic development and dye release can, in certain instances, cause the development process to shut down too rapidly. If the terpolymer described by Hannie is dissolved in an organic solvent and coated as a single layer, rather than as a polymer latex, it would result in the development process shutting down too slowly.
In U.S. Pat. No. 4,061,496, issued Dec. 6, 1977, Hannie et al describe a barrier layer comprising two adjacent barrier layers. One of the barrier layers comprises a polymeric latex having an activation energy of penetration to aqueous alkaline solution of less than 18 kcal/mole, such as a mixture of cellulose acetate and maleic anhydride, and the second layer is a polymeric latex having an activation energy of penetration to aqueous alkaline solution of greater than 18 kcal/mole, such as poly(methylacrylate-co-itaconic acid-co-vinylidene chloride). Although the barrier layer of Hannie et al shuts down development at a rate such that development at higher and lower temperatures does not vary greatly, even better temperature latitude is desirable. Further, the addition of a latex layer can be an economic disadvantage if it is to be coated over an organic solvent-coated layer. This prior art barrier layer also involves coating two layers, as opposed to coating a single timing layer, constituting a further expense to the manufacturer.
It is thus seen that barrier layers providing improved temperature latitude which are coatable in a single layer as solutions in organic solvents are extremely desirable from an economic point of view. It is further seen that such barrier layers should also have a rate of breakdown by aqueous alkaline solutions compatible with the rates of the accompanying photographic reactions.